Section 3.
GAS SYSTEMS
1. MIXED GAS BREATHING SYSTEMS. The correct gas mixture of helium, oxygen,
and nitrogen for missions under high pressure (greater than 300 feet) is
supplied to the PV by the gas system. The basic elements of the gas system
are shown in Figure 6-13.
2.
TRUCK TRANSFER. Delivery of the large volumes of pure helium, oxygen,
and nitrogen required for saturation diving are made by truck trailers. The
hyperbaric facility design should provide easy access for the trailer to the
transfer position. A truck trailer drive-through road or access at the
transfer position is desirable. Transfer of gas by the equalizing method
followed by the pumping method through a compressor or pump is shown in
Figure 6-14.
3.
GAS STORAGE. Three gasses are usually stored for mixed-gas dives:
oxygen, helium, and heliox mixture. Storage volumes are determined by depth,
chamber mission time (descent time, bottom time, and decompression time),
breathing gas composition requirements, and number of divers. In addition,
there must always be available an adequate back-up storage of all gas for
both breathing and pressurization to complete the decompression schedule from
maximum chamber pressure, including sufficient gas for possible stages of
repressurization or recompression.
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